1. Field of the Invention
The present invention relates to x-ray devices. Specifically, the present invention relates to an apparatus for providing automatic film exposure control to control the optical density in x-ray film radiographs to compensate for attenuation caused by a subject under examination.
2. Background of Related Art
It is a desired capability for modern x-ray systems to provide some sort of attenuation compensation. Such systems should have a capability to compensate for attenuation caused by different subjects to optimize the exposure for those particular subjects. For example, large-mass objects may require large amounts of x-ray radiation in order to perform an x-ray exposure which have sufficient optical density for the quality desired. Smaller massed objects, in contrast, may not require as much x-ray radiation in order to create the same optical density in the resulting image. Attenuation compensation is a desired capability in x-ray systems since overexposure or underexposure of an x-ray image essentially ruins the image for any useful diagnostic purpose. Additional exposures may thus have to be performed, exposing the subject to more radiation than would otherwise have been required.
Some prior art systems have utilized a technique for attenuation compensation which allows the operator to select, using a selector dial or a series of pushbuttons, a particular attenuation level. In other words, the exposure may be optimized for a large attenuator (e.g., a full-grown adult) or a small attenuator (e.g., a child). Operators of such prior art x-ray apparatus thus make subjective judgments on the attenuation based upon their estimation of the patient thickness. It is hoped that the operator accurately selects the proper attenuation to optimize the optical density of the exposure. These systems suffer from the disadvantage that the operator is forced to make a subjective judgment about the amount of attenuation caused by the subject. These devices also suffer from a cluttered control panel of the x-ray apparatus providing for a less user-friendly design. It is thus desired to control the variance and optical density of exposures within very specific parameters to optimize picture quality. Attenuation compensation is also increasingly a requirement in specifications for modern x-ray systems. Consistency of optical density is desired and may be optimized by the use of an exposure control system which regulates the amount of radiation reaching the film, as passed through an attenuator (e.g., a subject under examination). Such a system would provide many advantages over the prior art apparatus for attenuation control in an x-ray imaging system.